Gas turbine engines generally include a gas generator comprising: a compressor section with one or more compressors for compressing air flowing through the engine, a combustor in which fuel is mixed with the compressed air and ignited to form a high energy gas stream, and a turbine section which includes one or more rotors for driving the compressor(s). Many engines further include an additional turbine section, known as a power turbine, located aft of the gas generator which extracts energy from the gas flow out of the gas generator to drive an external device such as a fan or a propeller.
Each of the turbines and compressor include one or more bladed rows. Such rows will typically be alternately spaced with interposed vane rows or with counterrotating bladed rows. In either case, alternating rows extend into a flowpath from outer and inner annular casings, respectively.
Individual blades in each row are generally detachable from such casings and mountable therein. Numerous configurations are known for mounting blades in casings. For example, a common configuration includes a circumferential dovetail base which mates with a circumferential recess in the casing. In order to load such blades into the casing, it is known to cut or split the casing axially thereby forming two semicircular casing halves. Blades may then be loaded directly into the circumferential slots at the axial split. After the blades are loaded into each half, the casings are rejoined and fastened with a number of bolts through an axial flange. However, such flanges and bolts add increased weight to the casing structure and may cause out-of-round distortion of the casing with imposed thermal and mechanical operating loads.
An alternative way of assembling blades into a casing is to assemble one row at a time. For example, blades may be mounted in a single hoop forming part of either an outer or inner casing. Casing/airfoil assemblies may then be built up by "stacking" subsequent rows thereon. These assemblies again require numerous fasteners such as bolted flange joints which significantly increase the weight of the assembly.